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1.
The photolysis of water vapor on the surface of titanium coated polycrystalline n-TiO 2 at a temperature of 380°C is reported. A quantum conversion efficiency for hydrogen production of 2% is measured for excitation above the band gap of TiO 2. The experiments demonstrate the catalytic nature of the reaction with respect to the active material and also suggest an important role played by the titanium metal in the observations. 相似文献
2.
The reactions between SO 2 and O 2 were carried out in the presence of TiO 2 and NiO under various partial pressures of SO 2 and O 2 at temperatures from 240 to 330°C. TiO 2 and NiO were pretreated by applying an annealing effect from which the catalysts would have the different activity. The rates are the highest for TiO 2 pretreated at high temperature in the region of 400 to 600deg;C in vacuum, 1.21 × 10 ?4 mmHg. In contrast, the rates are the lowest for NiO pretreated at high temperaturefrom 350 to 550°C. The data have been correlated with 1.4 and first-order kinetics for TiO 2 and NiO, respectively. A reaction mechanism to explain the data was suggested. The quantities of anionic vacancies in TiO 2 surfaces and of positive holes in NiO appeared to be paramount in determining the type of kinetics. 相似文献
3.
When the anatase form of TiO 2 was heated at a constant rate of 6°C/min to 450°C it crystallized from hydrated amorphous TiO 2 gel at 170°C in pure water or at <150°C in NaOH solutions. The uptake of Na + ions into crystallized anatase affected the reactions subsequent to this initial crystallization while only anatase crystals continued to grow with increasing temperature in pure water. Immediately after the nearly amorphous second stage at 325°C, conversion from colloidal anatase particles to square sheet-shaped bronze-type TiO 2 crystals began at 350°C and was complete at 425°C in 0.5 M NaOH. This conversion was considered to proceed via crystallographic shear rather than via dissolution and precipitation since this also happened with thermal treatment to 700°C in air. 相似文献
4.
High-chromium vanadium–titanium magnetite (HCVTM) is a good valuable resource with high iron content in the form of complex iron ore which contains various valuable metal elements such as iron, vanadium, titanium, chromium. Direct reduction of HCVTM is studied based on thermodynamic analysis. Combined TG experimental verification and equilibrium calculation model was used to analyze the reaction sequence and equilibrium amount in this paper. The contents in HCVTM reduction system are simplified as 18 kinds of chemical compositions. Reductions of Fe3O4 and FeO·TiO2 are the main reduction reactions and are mainly reduced by C. The reduction reaction sequence of FeO·TiO2 is FeO·TiO2, TiO2, TiC, and Ti; the reduction reaction sequence of Fe3O4 is Fe3O4, FeO, and Fe. The minimum reduction temperature of HCVTM is 860 °C. The reduction of Cr is difficult to implement, and the minimum reduction temperature of V is above 700 °C. The gas phase in this system is mainly CO when the temperature is above 1000 °C. CO partial pressure curve of gasification reaction is in the shape of ‘S’ with increase of temperature. When the temperature is 1350 °C, C/O is 1.0 and reduction time is 30 min, HCVTM can be reduced thoroughly and the reduction degree can reach to 0.98. When C/O is lower than 1.0, FeTi2O5 is the reduction intermediate products from FeO·TiO2. When C/O is 1.0, diffraction peaks of Fe3O4 and FeO·TiO2 disappear, and they are reduced to Fe and TiO2. 相似文献
5.
A new efficient method for the synthesis of extended micro-and nano-sized crystals (whiskers, fibers) of titanium glycolate Ti(OCH 2CH 2O) 2 has been suggested. The method implies the reaction of hydrated titanium dioxide with ethylene glycol on heating in air. Thermolysis of Ti(OCH 2CH 2O) 2 in air gives titanium dioxide as anatase (400–500°C) and rutile ( T > 700°C), the morphology of titanium glycolate crystals being inherited by the oxide. The pseudocrystals of the thermolysis product in an inert gas medium ( T = 500–950°C) represent aglomeration of nano-sized titanium dioxide particles and amorphous carbon. At temperatures up to 1300°C, the formation of the TiO 2?x C x phase with a rutile structure is probable. In a wet air environment, titanium glycolate is partially hydrolyzed to give TiO x (OCH 2CH 2O) 2?2x (OH) 2x · xH 2O (0 ≤ x ≤ 1) and on keeping in water at room temperature, ethylene glycol is completely displaced from the crystals. This process is also not accompanied by changes in the particle morphology. 相似文献
6.
Combined structure of anodic TiO 2 nanotubes and TiO 2 nanoparticles (TiNTs-TiNPs) has been synthesized by a facile combination of hydrothermal and chemical vapor deposition methods. Ordered TiO 2 nanotubes with smooth walls were fabricated by two step anodization method in ethylene glycol containing NH 4F at 50 V. This nanotubular array after annealing at 450 °C was subjected to the hydrothermally produced gaseous environment in an autoclave with diluted TiCl 4 solution at its bottom. Vapors of TiCl 4 were allowed to react chemically with water vapors for predefined time durations at 180 °C that resulted in the deposition of TiO 2 nanoparticles on tubes’ surface and side walls. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed that for one hour reaction duration, nanoparticles were evenly coated on the walls of nanotubes, whereas, longer durations tend to deteriorate the tubular structure. Consequently, the ordered TiNTs-TiNPs array produced after one hour coating has shown better performance for dye-sensitized solar cell DSSC) in back illumination mode with 130% increase in efficiency as compared to the device based on bare TiO 2 nanotubes. The same photoanode has higher reflective properties with higher scattering ability. The solar cell based on this photoanode exhibits higher external quantum efficiency and effective charge transport properties. This study shows that porous ordered 1D structures based on TiO 2 are of crucial importance for the high performance of DSSCs. 相似文献
7.
Gas-phase catalytic and photocatalytic decomposition of ozone (O 3) was investigated using TiO 2 and Pt-loaded TiO 2 (Pt/TiO 2) at room temperature and atmospheric pressure. The nominal weight loading of Pt was less than 1 wt.%. Results of this study indicate that both the overall conversion of O 3 to O 2 and other products with UV irradiation and without UV irradiation (dark reaction) can be improved by using Pt-loaded TiO 2. Photocatalytic conversion of O 3 on pure TiO 2 decreased with increasing water vapor. In contrast, Pt/TiO 2 was active for the decomposition of ozone under the humidity condition at room temperature. 相似文献
8.
The solid state reactions between TiO 2 and Na 2S 2O 8 or K 2S 2O 8 have been investigated using TG, DTG, DTA, IR, and X-ray diffraction studies in the range of 20 to 1000°C.It has been shown that TiO 2 reacts stoichiometrically (1 : 1) with Na 2S 2O 8 in the range of 160 and 220°C forming the complex sodium monoperoxodisulfato—titanium(IV) as characterized by IR and X-ray analysis. The new complex then decomposes into the reactants above 190°C.An exothermic reaction has been observed between TiO 2 and molten K 2S 2O 7 at mole ratio 1:2 respectively and higher, in the range of 280 and 350°C. The IR and X-ray analyses have shown the formation of a complex namely, potassium tetrasulfato titanium(IV) for which the formula and structure have been proposed. This complex decomposes at higher temperatures into K 2SO 4 and a mixed sulfate of potassium and titanium. The mixed sulfate melts at 620°C and decomposes into K 2SO 4, TiO 2, and the gaseous SO 3.On the other hand, Na 2S 2O 8 decomposes in a special mode producing a polymeric product of Na 10S 9O 32. Decomposition of this species occurs after melting at 560°C into Na 2SO 4 and sulfur oxides. The decomposition reaction has been proved to be catalysed by TiO 2 itself. 相似文献
9.
Thin sol–gel TiO 2 layers deposited on the conductive ITO glass by means of three various deposition techniques (dip-coating, inkjet printing and spray-coating) were used as photoanode in the three-compartment electrochemical cell. The thin TiO 2 films were treated at 450 °C and after calcination all samples possessed the crystallographic form of anatase. The relationship between surface structure and photo-induced conductivity of the nanostructured layers was investigated. It was found that the used deposition method significantly influenced the structural properties of prepared layers; mainly, the formation of defects and their quantity in the prepared films. The surface properties of the calcined layers were determined by XRD, Raman spectroscopy, SEM, AFM, UV–Vis analyses and by the optical microscopy. The photo-induced properties of nanoparticulate TiO 2/ITO photoanode were studied by electrochemical measurements combined with UV irradiation. 相似文献
10.
Perovskite solar cells have garnered and held international research interest, due to ever-climbing power conversion efficiency values, now >25 %. Some high efficiency configurations utilize a compact TiO 2 layer underneath a mesoporous TiO 2 layer, both of which require high temperature annealing steps that could hinder perovskite commercialization. To address the high thermal budget, we chose to use inkjet-printing to combine the two layers into a single TiO 2 film, which incorporates both nanoparticle and molecular precursor as well as organic fullerene additives. We printed the ink on fluorine-doped tin oxide, and after annealing at various temperatures, we found that 400 °C was the optimum annealing temperature for the inkjet-printed electron transport layers, which is significantly lower than the 500 °C required to anneal typical mesoporous TiO 2 films. 相似文献
11.
Highly ordered TiO 2 nanotube arrays were fabricated on a conducting glass substrate in NH 4HF 2/glycol electrolyte via anodization of titanium film which was deposited by direct current magnetron sputtering (DCMS) at different temperatures. The results showed that Ti films with good homogeneity and high denseness could be formed under the conditions Ar pressure 0.35 Pa, direct current 3.5 A, and 2 h at 300 °C. Characterization of the TiO 2 nanotube arrays was investigated comparatively, by altering anodization time. The surface morphology of the samples changed as the anodization time was prolonged from 10 to 150 min at 30 V. The TiO 2 thin film was amorphous and could be transformed into anatase by annealing at 450 °C. On the basis of UV?Cvisible transmission spectra the bandgap of the thin film was calculated to be 3.12 eV, and its tail extended to 2.6 eV. 相似文献
12.
In this work, a nonaqueous method is used to fabricate thin TiO 2 layers. In contrast to the common aqueous sol–gel approach, our method yields layers of anatase nanocrystallites already at low temperature. Raman spectroscopy, electron microscopy and charge extraction by linearly increasing voltage are employed to study the effect of sintering temperature on the structural and electronic properties of the nanocrystalline TiO 2 layer. Raising the sintering temperature from 120 to 600?°C is found to alter the chemical composition, the layer’s porosity and its surface but not the crystal phase. The room temperature mobility increases from 2?×?10 ?6 to 3?×?10 ?5?cm 2/Vs when the sinter temperature is increased from 400 to 600?°C, which is explained by a better interparticle connectivity. Solar cells comprising such nanoporous TiO 2 layers and a soluble derivative of cyclohexylamino-poly( p-phenylene vinylene) were fabricated and studied with regard to their structural and photovoltaic properties. We found only weak polymer infiltration into the oxide layer for sintering temperatures up to 550?°C, while the polymer penetrated deeply into titania layers that were sintered at 600?°C. Best photovoltaic performance was reached with a nanoporous TiO 2 film sintered at 550?°C, which yielded a power conversion efficiency of 0.5?%. Noticeably, samples with the TiO 2 layer dried at 120?°C displayed short-circuit currents and open circuit voltages only about 15–20?% lower than for the most efficient devices, meaning that our nonaqueous route yields titania layers with reasonable transport properties even at low sintering temperatures. 相似文献
13.
High-temperature treatment steps in fabrication process of dye sensitized solar cell (DSSC) significantly contribute to the manufacturing costs and limit the use of temperature sensitive substrates. Therefore our aim was to develop a simple method for the preparation of water-based TiO 2 paste. The paste is based on peroxotitanic acid (PTA) sol–gel matrix and commercial TiO 2 nanoparticles (P25). Two fabrication processes to decompose/transform the PTA matrix in the printed TiO 2 layer are explored and combined: annealing at temperatures up to 250 °C and/or oxygen plasma treatment. The results show that the PTA matrix in the paste converts to anatase phase and to some extent also attaches to the TiO 2 nanoparticles P25 acting as an interconnecting network within TiO 2 layer. The transformation of the PTA matrix occurs around 250 °C, but in the presence of TiO 2 nanoparticles P25 it starts already at 120 °C. In addition the results reveal that the crystallization is achievable also solely with the oxygen plasma treatment. The efficiency of the TiO 2 layers, exposed to different post-deposition treatments, is evaluated in DSSCs. The results show that oxygen plasma treatment of the TiO 2 layers could efficiently replace temperature curing at 250 °C. Within this study the DSSCs with the efficiency up to 4.2 % measured under standard test conditions (1,000 W/m 2, AM1.5, 25 °C) were realized. 相似文献
14.
In this study, a TiO 2 film was prepared in an annular reactor by the chemical vapor deposition (CVD) method. Results indicated that anatase crystals
were formed, except for at a deposition temperature of 200°C without calcination. At a calcination temperature of 850°C, anatase
crystal was the major species formed with a small amount of rutile crystals. After conducting a photocatalytic reaction of
toluene, the best activity was found with a preparation temperature of 350°C for the deposition, and 550°C for calcination. 相似文献
15.
Nanosized TiO 2 particles were prepared by the hydrothermal method from the amorphous powders which were precipitated in an aqueous peroxotitanate
solution. The physical properties of the nanosized TiO 2 particles prepared were investigated. We also examined the activity of TiO 2 particles as a photocatalyst on the decomposition of orange II. The titania sol can be successfully crystallized to the anatase
phase through hydrothermal aging at temperatures higher than 160°C. The particle size increases from 18 to 26 nm as the synthesis
temperature increases from 140 to 200°C. Titania particles prepared at 180°C show the highest activity, and titania particles
calcined at 400°C show also the highest activity on the photocatalytic decomposition of orange II. 相似文献
16.
Composites of (001)‐face‐exposed TiO 2 ((001)‐TiO 2) and CuO were synthesized in water vapor environment at 250°C with various Cu/Ti molar ratios ( RCu/Ti). The resulting CuO/(001)‐TiO 2 composites were characterized using a variety of techniques. The synthesis under high‐temperature vapor allows close contact between CuO and (001)‐TiO 2, which results in the formation of heterojunctions, as evidenced by the shift of valence band maximum towards the forbidden band of TiO 2. An appropriate ratio of CuO can enhance the absorption of visible light and promote the separation of photogenerated carriers, which improve the photocatalytic performance. The degradation rate constant Kapp increased from 5.5 × 10 ?2 to 8.1 × 10 ?2 min ?1 for RCu/Ti = 0.5. Additionally, the results showed that superoxide radicals ( ?O 2?) play a major role in the photocatalytic degradation of methylene blue. 相似文献
17.
In this project, we synthesized TiO 2 compounds through the molten salt method (MSM) using Ti(IV) oxysulfate, as the Ti source. Molten salts in the ratio of 0.375 M LiNO 3:0.180 M NaNO 3:0.445 M KNO 3 were added and heated at temperatures of 145, 280, 380, and 480 °C for 2 h in air, respectively. A part of the sample prepared at 145 °C was further reheated to 850 °C for 2 h in air. X-ray diffraction studies showed that the amorphous phase was obtained when the sample was prepared at 145 °C, and polycrystalline to crystalline anatase phase was formed when heated from 280 to 850 °C, which is complementary to the results of selected area electron diffraction studies. Electrochemical properties were studied using galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy at a current density of 33 mA g ?1 (0.1 C rate) and a scan rate of 0.058 mV s ?1, in the voltage range 1.0–2.8 V vs. Li. Electrochemical cycling profiles for the amorphous TiO 2 samples prepared at 145 °C showed single-phase reaction with a low reversible capacity of 65 mAh g ?1, whereas compounds prepared at 280 °C and above showed a two-phase reaction of Li-poor and Li-rich regions with a reversible capacity of 200 mAh g ?1. TiO 2 produced at 280 °C showed the lowest capacity fading and the lowest impedance value among the investigated samples. 相似文献
18.
A series of composite photocatalysts based on titanium dioxide deposited on the surface of a zirconium phosphate support were
synthesized under different synthesis and heat-treatment conditions. The study of the photodestruction kinetics of Rhodamine
C showed that the synthesized composites possess high photocatalytic activity that is competitive with the activity of a commercial
Hombikat UV100 photocatalyst. The composites based on zirconium phosphate treated with isopropanol at the precipitation stage
whereupon heated at 550°C exhibit the highest photocatalytic activity after heating at 750°C. It was found that such zirconium
phosphate support has the largest specific surface area (270 m 2/g). After heating at 550°C, the surface becomes more stable to the subsequent heating to 750°C, which is necessary for the
most complete crystallization of TiO 2 ensuring its high photocatalytic characteristics. 相似文献
19.
The effect of the state of hydrated surface of the bulk oxide photocatalysts, TiO 2, CeO 2, and ZnO on the rate of UV-induced oxidation of CO with atmospheric oxygen was studied. The activity of dehydroxylated catalyst samples evacuated at temperatures of >350 °C toward CO photooxidation decreases in the series CeO 2 > ZnO ≈ TiO 2, while that of partially hydrated samples after pretreatment at 20 °C changes in the order TiO 2 > ZnO ≥ CeO 2 ≈ 0. According to the results, the difference in the photocatalytic activity toward CO oxidation on the dehydrated ZnO, TiO 2, and CeO 2 catalysts is attributable to different concentrations of oxygen vacancies, which are formed more readily after high-temperature treatment on ZnO and CeO 2 and thus promote higher rate of CO photooxidation. Using a new technique for recording transmittance IR spectra, it was found that photoirradiation in the presence of adsorbed water and O 2 gives peroxides and hydroperoxides, with their concentrations decreasing in the series TiO 2 >> ZnO >> CeO 2. Most likely, these species are active intermediates of CO photooxidation with oxygen in the presence of adsorbed water. The hydrophobization effect was detected upon TiO 2 modification with zinc, resulting in removal of surface acid sites capable of adsorbing water. The TiO 2 modification with zinc increases the activity of CO photooxidation with respect to the oxidation catalyzed by samples pretreated at low temperatures (20—60 °C). 相似文献
20.
Monodispersed TiO 2 hybrid microspheres were prepared via the hydrolysis of titanium isopropoxide (TTIP) in ethanol solution containing p-aminophenylacetic acid (APA). The effects of the APA:TTIP molar ratio, water content, reaction time and reaction temperature on the morphology of the resultant spheres were investigated. The products were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. It was demonstrated that the diameters of the resultant TiO 2 spheres could be tuned in the range of 380–800 nm by changing the APA:TTIP molar ratio (1:3 to 3:1) and water content (1–3 v/v%) in the reaction medium, and that increasing the APA:TTIP molar ratio led to larger TiO 2 hybrid spheres while increasing the water content decreased their size. The loading content of APA in the hybrid spheres could reach 20 wt.% as they were prepared with the APA:TTIP ratio of 3:1. The possible formation mechanism of the hybrid spheres was also investigated. It was found that APA slowed down the hydrolysis rate of the titanium precursor so that resulted in the formation of the TiO 2 spheres. In addition, the APA present in TiO 2 spheres acted as a reducing agent to in situ convert HAuCl 4 into metallic Au on the surface of the TiO 2 spheres. The catalytic activity of the resultant Au/APA–TiO 2 composite was examined using transfer hydrogenation of phenylacetone with 2-propanol, and it was indicated that the catalyst displayed high efficiency for this reaction. 相似文献
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